EGAD

Zero-Tech Solar Still

A solar still made with pottery-age technology, shown in cross-section.

Let's say you're stranded on a desert island, and you've found an outcropping of clay and a way to make fire, but your water supply is unreliable. You might make an item along the lines of the pot I've sketched here. Then you'd fill the outer ring with seawater, close the lid, and put more seawater in the depression atop the lid. Place in a sunny location or on the hottest sand you can find -- the coals of your campfire would probably work nicely, too. The point is to get the bottom hot, while evaporation keeps the lid cool, so condensation forms and drips into the central catchbasin. When finished, find a reed or similar to use as a straw and drink your freshly distilled water.

The caveat is that this is about the most inefficient way you could possibly do this, having no metal or glass to work with. In particular, since you're not recycling the latent heat of condensation, you have to supply the heat from outside. With solar energy this pot will be limited to around a tenth of a liter per day, so you'll have to make a bunch.

I think at least one reader knows why I'm posting this.